System and method for providing automated sample preparation for plan view transmission electron microscopy

ABSTRACT

A system and method is described for providing automated sample preparation for plan view transmission electron microscopy. A sample wafer is microcleaved from a semiconductor wafer and mounted on a first support stub. Then the sample wafer is cut with an automated diamond sawing tool to expose a cross sectional view of the sample wafer. The sample wafer is removed from the first support stub and rotated to orient the sample wafer for plan view imaging. The rotated sample wafer is then remounted on a second support stub and cut with the automated diamond sawing tool to expose a plan view surface of the rotated sample wafer. The remounted sample wafer is subsequently prepared for focused ion beam (FIB) milling and plan view transmission electron microscopy imaging.

This application is a continuation of prior U.S. patent application Ser.No. 10/903,367 filed on Jul. 30, 2004, now U.S. Pat. No. 7,250,318.

TECHNICAL FIELD OF THE INVENTION

The present invention is generally directed to manufacturing technologyfor semiconductor circuits and, in particular, to a system and methodfor providing automated sample preparation for plan view transmissionelectron microscopy.

BACKGROUND OF THE INVENTION

Increasingly smaller geometries and feature sizes of semiconductordevices have made transmission electron microscopy (TEM) an increasingimportant characterization technique for semiconductor productdevelopment and failure analysis. Resolution of less than fifteenhundredths of a nanometer (0.15 nm) allows TEM to provide structuralinformation down to the atomic level. TEM can also be used inconjunction with X-ray or electron energy loss spectrometers to provideinformation on chemical composition at sub-nanometer length scales. See,for example, D. B. Williams and C. B. Carter, Transmission ElectronMicroscopy. A Textbook for Materials Science, Plenum Press, New York,1996.

The chief difficulty associated with TEM has traditionally been thepreparation of samples. D. K. Schroeder, Semiconductor Material andDevice Characterization, Second Edition, John Wiley & Sons, New York,1998. Samples for TEM analysis must be less than two hundred fiftynanometers (250 nm) thick in order to achieve good image quality. Theincreasing demand for TEM analysis in the semiconductor industry hasplaced a high priority on reducing the time and labor required toprepare a TEM sample.

One of the earliest techniques for preparing TEM samples fromsemiconductor materials is mechanical lapping-polishing. S. J. Klepieis,J. P. Benedict and R. M. Anderson, Specimen Preparation for TransmissionElectron Microscopy of Materials, Materials Research Society SymposiumProceedings 115, p. 179, Materials Research Society, Pittsburgh, Pa.,1988. In mechanical lapping-polishing a small piece of semiconductorwafer containing the sample site is mounted on a tripod polisher. Thetripod polisher holds the wafer against a rotating abrasive disc. Aseries of progressively finer abrasives are used with water rinse toreduce the sample to electron transparency. The mechanicallapping-polishing technique typically takes four to five hours tocomplete. The mechanical lapping-polishing technique can be used toprepare both plan-view samples and cross-sectional samples of asemiconductor wafer. FIG. 1 illustrates a schematic view of one half ofan exemplary prior art semiconductor wafer 100 showing an exemplaryportion of a plan-view 110 of the wafer 100 and an exemplary portion ofa cross-sectional view 120 of the wafer 100.

The prior art mechanical lapping-polishing technique can also beperformed automatically. Sagitta Corporation has developed an automatictool for mechanically lapping-polishing both TEM samples and ScanningElectron Microscopy (SEM) samples. G. A. Schechter, L. Adams, and I.Ward, SEM/TEM Sample Preparation, Solid State Technology, pp. S1-S8,September, 2000. The Sagitta automatic tool speeds up the polishingprocess by removing all of the manual inspections required to check theprogress during the tripod polishing process in order to avoid polishingaway the site of interest.

The past fifteen (15) years have seen a trend toward the increased useof focused ion beam (FIB) milling tools for the preparation of TEMsamples. Site-specific TEM samples can be prepared faster and easierusing an FIB milling tool than by polishing. FIB preparation istypically done with a dual beam instrument employing an ion column formilling and an SEM column for imaging. The ion column uses a beam ofgallium ions to remove unwanted material and expose a fresh surfacepassing through the region of interest. Progress is monitored withsecondary electron images taking throughout the milling process.

Several techniques have been developed to make FIB-milledcross-sectional samples compatible with the standard three millimeter (3mm) diameter TEM sample holder. One such technique is to use tripodpolishing for the initial sizing of the sample. R. Anderson and S. J.Klepeis, Specimen Preparation for Transmission Electron Microscopy ofMaterial IV, Materials Research Society Symposium Proceedings V.480, p.187, Materials Research Society, Pittsburgh, Pa., 1997. In this approachthe sample is polished to a thickness of approximately thirty microns(30 μm) and then mounted on a modified copper support grid that iscompatible with milling in the FIB and with the TEM sample holder. Priorto use, the sample holder grid is modified by manually cutting away oneparallel side to allow access for the ion beam during the millingprocess. Finally, the sample is transferred into an FIB instrument forultimate thinning to electron transparency. This approach can be usedfor both plan-view samples and cross-section samples.

Another approach for making FIB preparation compatible with TEM sampleholders is a technique known as “μ-sampling”. This approach involves thetransfer of FIB-milled TEM samples directly from a semiconductor chip orwafer onto a copper support grid using micro-manipulators. See, forexample, M. H. F. Overwijk, F. C. van den Heuvel, and C. W. T.Bulle-Lieuwma, Journal of Vacuum Science and Technology, B11, p. 2021(1993); L. A. Giannuzzi, J. L. Drown, S. R. Brown, R. B. Irwin, and F.A. Steive, Materials Research Society Symposium Proceedings, Volume 480on Specimen Preparation for Transmission Electron Microscopy ofMaterials IV, p. 19, American Institute of Physics, New York, 1997; L.A. Giannuzzi, J. L. Drown, S. R. Brown, R. B. Irwin, and F. A. Steive,Micros. Res. Tech. 41, p. 285, 1998; and T. Onishi, H. Koike, T.Ishitani, S. Tomimatsu, K. Umemura, and T. Kamino, A New Focused-IonBeam Microsampling Technique for TEM Observation of Site-Specific Areas,Proceedings of the Twenty Fifth International Symposium for Testing andFailure Analysis, pp. 449-453, 1999.

The “μ-sampling” technique avoids many of the “pre-preparation” stepssuch as wafer cleaving, sawing, and tripod polishing, but it does so atthe expense of increased time spent on the FIB preparation of thesample. The high cost and heavy usage commonly associated with FIBinstruments make any increase in instrument time for sample preparationa potential factor in bottlenecking laboratory output.

A third approach for making FIB preparation compatible with TEM sampleholders is a technique developed by the Semiconductor EngineeringLaboratories Corporation (SELA) The technique will be referred to as the“SELA process”. A more detailed discussion of the SELA process is setforth in W. D. Kaplan, R. Oviedo, K. Kisslinger, E. M. Raz and C. Smith,Automatic TEM Sample Preparation, Proceedings of the Twenty FifthInternational Symposium for Testing and Failure Analysis, pp. 103-107,1999; and in R. Reyes, F. Shaapur, D. Griffiths, A. C. Diebold, B.Foran, and E. Raz, Automated SEM and TEM Sample Preparation Applied toCopper/Low K Materials, AIP Conference Proceedings, pp. 580-585, 2001.

The SELA process automates the initial wafer cleaving and thinning stepsfor cross-sectional semiconductor sample preparation. The SELA processproceeds in two steps. In the first step an automated microcleaver isused to cut the samples. The automated microcleaver has an accuracy ofone fourth of a micron (0.25 μm). In the second step the samples thatare output from the automated microcleaver are then provided to a rotarydiamond saw (referred to as a “TEMpro™” unit). An earlier version of theTEMpro™ unit is referred to as a “TEMstation™” unit. “TEMpro™” and“TEMstation™” are trademarks of the Semiconductor EngineeringLaboratories Corporation (SELA).

The two SELA tools (i.e., the automated microcleaver and the rotarydiamond saw (“TEMpro™”)) automatically mount the sample on aTEM-compatible copper support grid and use a series of diamond saws toreduce the sample to an approximate thickness of thirty microns (30 μm).The result is a TEM-compatible, site-specific, cross-section sample thatis ready for FIB milling. By consistently and quickly achieving a samplethickness of thirty microns (30 μm) the SELA process is aimed at a highthroughput of TEM samples by eliminating the steps of tripod polishingand by minimizing FIB instrument time.

The prior art SELA process provides automated sample preparation forobtaining cross-sectional views of transmission electron microscopy.However, there is no similar method for preparing samples for plan viewtransmission electron microscopy.

There is therefore a need in the art for a system and method forproviding automated sample preparation for plan view transmissionelectron microscopy. There is also a need in the art for a system andmethod that automatically prepares plan view transmission electronmicroscopy samples in manner that is not labor intensive.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention to provide a system and methodfor providing automated sample preparation for plan view transmissionelectron microscopy (TEM).

In one advantageous embodiment of the method of the invention a samplewafer is microcleaved from a semiconductor wafer. The sample wafer isthen mounted on a first copper support stub. Then the sample wafer iscut with an automated diamond sawing tool to expose a cross sectionalview of the sample wafer. The sample wafer is then removed from thefirst copper support stub and rotated to orient the sample wafer forplan view imaging. The sample wafer is rotated ninety degrees (90°) toorient the sample wafer for plan view TEM imaging.

The rotated sample wafer is then remounted on a second copper supportstub and returned to the automated diamond sawing tool. The automateddiamond sawing tool then cuts the rotated sample wafer to expose a planview surface of the rotated sample wafer. The remounted sample wafer isthen prepared for subsequent focused ion beam (FIB) milling andsubsequent plan view TEM imaging.

The processing time required for performing the method of the presentinvention is approximately forty (40) minutes. This amount of time isapproximately twice as long as the processing time required for thestandard SELA process for cross-sectional TEM samples. The processingtime required by the present invention represents a substantial timesaving when compared to the processing time required for the prior artmethods of preparing plan view samples using tripod polishing. Theprocessing time required by the present invention also represents asubstantial time saving when compared to the processing time requiredfor the prior art method of polishing plan view samples in preparationfor FIB milling.

The automated nature of the method of the present invention also allowslaboratory personnel to work on other tasks while the SELA tools areoperating. The possibility of the laboratory personnel being able to“multitask” in this manner does not exist in the case of the prior artprocesses (e.g., mechanical lapping-polishing).

It is an object of the present invention to provide a system and methodfor providing automated sample preparation for plan view TEM imaging.

It is also an object of the present invention to provide a system andmethod for rotating a sample wafer to orient the sample wafer for planview TEM imaging.

It is yet another object of the present invention to provide a systemand method for remounting a rotated sample wafer on a spacer wafer on asecond copper support stub to prepare the sample wafer for plan view TEMimaging.

It is still another object of the present invention to provide a systemand method for the automated preparation of sample wafers for plan viewTEM imaging to allow laboratory personnel to be free to work on othertasks while the sample wafers of the present invention are automaticallybeing prepared.

It is another object of the present invention to provide sample wafersthat are rotated and remounted on a copper support stub in anorientation that facilitates plan view TEM imaging of the sample wafers.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that those skilled in the art maybetter understand the detailed description of the invention thatfollows. Additional features and advantages of the invention will bedescribed hereinafter that form the subject of the claims of theinvention. Those skilled in the art should appreciate that they mayreadily use the conception and the specific embodiment disclosed as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. Those skilled in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the invention in its broadest form.

Before undertaking the Detailed Description of the Invention below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior uses, as well as future uses, of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates a schematic view of one half of an exemplary priorart semiconductor wafer showing an exemplary portion of a plan-view ofthe wafer and an exemplary portion of a cross-sectional view of thewafer;

FIG. 2 illustrates an exemplary input sample wafer in the shape of arectangle cut from a microcleaver sample;

FIG. 3 illustrates the input sample wafer shown in FIG. 2 before it isglued to a copper support stub;

FIG. 4 illustrates the input sample wafer shown in FIG. 3 after it isglued to the copper support stub;

FIG. 5 illustrates the result of a first saw step performed on the inputsample wafer shown in FIG. 4;

FIG. 6 illustrates the result of a second saw step performed on theinput sample wafer shown in FIG. 5;

FIG. 7 illustrates the result of removing the input sample wafer fromthe copper support stub shown in FIG. 6;

FIG. 8 illustrates a spacer wafer and a new copper support stub to whichthe spacer wafer is to be glued;

FIG. 9 illustrates the result of gluing the spacer wafer to the newcopper support stub shown in FIG. 8;

FIG. 10 illustrates the transfer of the sample wafer shown in FIG. 7 tothe spacer wafer shown in FIG. 9;

FIG. 11 illustrates the result of gluing the sample wafer shown in FIG.10 to the spacer wafer shown in FIG. 10;

FIG. 12 illustrates a three quarter side view of the sample wafer afterthe sample wafer has been glued to the spacer wafer and remounted on acopper support stub;

FIG. 13 illustrates a top down view of the sample wafer after the samplewafer has been glued to the spacer wafer and remounted on a coppersupport stub;

FIG. 14 illustrates the result of applying a plan-view first saw cut tothe sample wafer shown in FIG. 11;

FIG. 15 illustrates the result of applying a plan-view second saw cut tothe sample wafer shown in FIG. 14;

FIG. 16 illustrates the result of clamping a focused ion beam (FIB)clamp to the sample wafer and copper support stub shown in FIG. 15;

FIG. 17 illustrates the sample wafer and copper support stub and FIBclamp as shown in FIG. 16 ready to receive a plan-view third saw cut toremove the copper support stub;

FIG. 18 illustrates the result of applying a plan-view third saw cut tothe sample wafer and copper support stub and FIB clamp shown in FIG. 17;

FIG. 19 illustrates an optical image of a first side of a completed TEMsample with circuitry correctly oriented for plan-view imaging;

FIG. 20 illustrates an optical image of a second side of the completedTEM sample shown in FIG. 19;

FIG. 21 illustrates an exemplary TEM image of an FIB-milled plan-viewTEM sample manufactured in accordance with the method of the presentinvention;

FIG. 22 illustrates a flow chart showing the steps of an advantageousembodiment of the method of the present invention;

FIG. 23 illustrates a flow chart showing a more detailed version of thesteps of a first portion of the method of the present invention shown inFIG. 22; and

FIG. 24 illustrates a flow chart showing a more detailed version of thesteps of a second portion of the method of the present invention shownin FIG. 22.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 through 24, discussed below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any type of suitably arranged device for preparingplan-view TEM samples.

To simplify the drawings the reference numerals from previous drawingsmay sometimes not be repeated for structures that have already beenidentified.

The automated plan-view TEM sample preparation method of the presentinvention comprises a four stage process. The four stages are: (1)microcleaving process, (2) initial sawing process, (3) remountingprocess, and (4) final sawing process. The resulting TEM samplecomprises a thirty micron (30 μm) thick section of silicon wafer gluedonto a TEM-compatible support grid, with circuitry containing the siteof interest exposed on the top surface. The sample is ready forplan-view FIB milling and subsequent TEM imaging. The figures describedbelow comprise a series of diagrams that illustrate the operations thatmake up the four stages of the method of the present invention.

MICROCLEAVING PROCESS. The first stage in the method of the presentinvention comprises a microcleaving process. The microcleaving processis accomplished using either the SELA MC500 automated microcleaver orits predecessor the SELA MC200 automated microcleaver (not shown in thefigures). The automated microcleaver uses point-and-click operatingsoftware and digital imaging to achieve very precise and accuratecleaving of the area of interest of a semiconductor wafer. The accuracyof the cleaving process is plus or minus one fourth of a micron (+/−0.25μm) For general background information on microcleaving refer to C.Smith, Microcleaving, European Semiconductor, January 1995.

Input to the SELA MC200 automated microcleaver is a section ofsemiconductor wafer that is eleven millimeters (11 mm) to thirteenmillimeters (13 mm) wide and forty millimeters (40 mm) to eightymillimeters (80 mm) long. The site of interest is typically located inthe middle third of the wafer section and not more than one millimeter(1 mm) in from an alignment edge. The user then selects a location forthe cleave, typically three microns (3 μm) to five microns (5 μm) fromthe site of interest. The automated microcleaver then proceeds to markthe selected location with a diamond scribe and then cleaves the waferat the selected location. The new cleave then becomes the prime edge forthe diamond saw TEMpro™ tool (or the diamond saw TEMstation™ tool). Themicrocleaving process usually takes fewer than fifteen minutes toperform.

INITIAL SAWING PROCESS. The second stage in the method of the presentinvention comprises an initial sawing process. The initial sawingprocess (and the subsequent remounting step and the final sawing processof the method) utilizes the SELA TEMpro™ diamond sawing tool (or itspredecessor the SELA TEMstation™ diamond sawing tool). The SELA diamondsawing tools were developed as high throughput automated devices forpreparing cross-sectional TEM samples from semiconductor wafers. TheSELA diamond sawing tools take microcleaved samples from the MC500automated microcleaver (or the MC200 microcleaver) as input and employ aseries of rotary diamond saws to reduce the sample to a size suitablefor rapid FIB milling. As part of this process the sample is mountedonto a copper disc compatible with most TEM sample holders. The processtime for the cross-sectional samples is typically fifteen to twentyminutes. The process time for the plan-view samples in accordance withthe principles of the present invention takes approximately twice aslong (i.e., thirty to forty minutes) as the process time for thecross-sectional samples.

In the first step of the initial sawing process the TEMpro™ diamond sawmakes a presaw cut. The presaw cut serves to remove the excess materialthat is required for the microcleaver. As shown in FIG. 2, the presawcut cuts a one and one half millimeter (1.5 mm) by three millimeter (3mm) rectangle 200 from the corner of the microcleaver sample 210. Thesite of interest is situated along the prime edge and forms one of theone and one half millimeter (1.5 mm) sides of the rectangle 200. Theoutput from the presaw cut is automatically glued to a copper supportstub 300, as shown in FIG. 3 and in FIG. 4. The copper support stub 300is mounted on a stub holder fixture 310. The copper support stub 300supports the sample 200 during subsequent wafer sawing operations andultimately helps to make output from the TEMpro™ diamond saw compatiblewith standard three millimeter (3 mm) diameter TEM sample holders.

Although the support stub 300 is stated to be a copper support stub 300,it is noted that the invention is not limited to the use of coppermaterial for the support stub. Any other suitable material may be usedin place of copper in the manufacture of a support stub.

The next step in the initial sawing process is referred to as the firstsaw step. FIG. 5 illustrates the first saw step. For cross-sectionalsamples the first saw step establishes the thirty micron (30 μm) widthof the wafer that remains as the completed TEMpro™ sample. Forpreparation of the plan-view samples, the first saw width is increasedto the maximum permissible width in the TEMpro™ diamond saw. The maximumpermissible width in the TEMpro™, diamond saw is presently approximatelyninety microns (90 μm). The software routine in the TEMpro™ diamond sawthat controls the maximum permissible width may be modified to increasethe maximum permissible width to more than ninety microns (90 μm) inorder to facilitate the preparation of plan-view TEM samples.

The first saw cut is intentionally made shallow in order to preserve theaccuracy and precision of the diamond blade used to cut the wafer. Thedepth of the first saw cut is approximately one hundred sixty microns(160 μm) and is not intended to cut the full thickness of the samplewafer 200.

The next step in the initial sawing process is referred to as the secondsaw step. Another diamond blade that is referred to as the second saw isused to complete the cut through the full thickness of the wafer 200 andalso through the copper support stub 300. The diamond blade of thesecond saw is coarser than the diamond blade of the first saw. Thecoarser diamond blade of the second saw is sufficiently accurate forcutting through the rest of the wafer 200 and through the copper supportstub 300. The result of the second saw step is shown in FIG. 6.

REMOUNTING PROCESS. The most important process modifications for thepreparation of plan-view samples occur after the initial saw process hasbeen completed. These modifications are required to re-position thesample wafer 200 relative to the TEMpro™ copper support stub 300 so thatthe completed sample 200 has its circuitry oriented correctly forplan-view imaging in TEM. The third stage in the method of the presentinvention comprises a remounting process. The software routine used tooperate the first saw cut and the second saw cut is terminated and thesample wafer 200 is unloaded from the TEMpro™ diamond saw.

The copper support stub 300 with the sample wafer 200 attached to it isthen removed from the stub holder fixture 310 and placed into a solutionof glue removal solvent. After soaking for about twenty five minutes inthe glue removal solvent (e.g., Loctite X-NMS Cleanup Solvent) thesample wafer 200 is completely freed from the copper support stub 300.This result is shown in FIG. 7. All traces of the glue removal solventare removed by soaking the sample wafer 200 for a few minutes in acetoneand then in isopropyl alcohol. The sample wafer 200 is then allowed toair dry.

Now the sample wafer 200 is ready to be glued to a fresh copper supportstub 800 in the proper orientation for plan-view imaging. The new coppersupport stub 800 is mounted on the stub holder fixture 310. Forplan-view imaging the sample wafer 200 is rotated ninety degrees (90°)so that the circuitry is on one side of the sample wafer 200, instead ofbeing edge-on as in the case of a cross-sectional sample wafer. Becausethe maximum width of the first saw cut is one hundred microns (100 μm),the rotated sample wafer 200 is not the standard wafer thicknessrequired for the TEMpro™ diamond saw.

In order to compensate for the difference in width, a spacer wafer 810is prepared from a one hundred millimeter (100 mm) diameter wafer with aone-zero-zero (100) lattice orientation. The spacer wafer 810 isapproximately four hundred eighty microns (480 μm) thick, so that thecombined thickness of the spacer wafer 810 and the sample wafer 200together is approximately five hundred seventy microns (570 μm). Thisthickness is a good match for the height of the ledge that holds thesample wafer 200 in the copper support stub 800. The use of a spacerwafer 810 can be dispensed with if a modification is made to the TEMpro™diamond saw to permit thicker first saw cuts. The spacer wafer 810 issubjected to the presaw cut in the TEMpro™ diamond saw. The spacer wafer810 is removed from the instrument after it has been glued to a newcopper support stub 800, as shown in FIG. 8 and in FIG. 9.

The remounting process is completed by transferring the sample wafer 200to the spacer wafer 810 as shown in FIG. 10 and then gluing the samplewafer 200 to the top of the spacer wafer 810 as shown in FIG. 11. Properorientation of the sample wafer 200 during this gluing step is criticalto insure that the target site is correctly positioned for plan-viewimaging. The sample wafer 200 is oriented with its microcleaved surfacefacing upwards and its circuitry pushed up against the vertical wall ofthe copper support stub 800. This positions the target site inside ofthe imaging window in the copper support stub 800. FIG. 12 shows a threequarter side view of the sample wafer 200 after the sample wafer 200 hasbeen glued to the spacer wafer 810 and remounted on a copper supportstub 800. FIG. 13 shows a top down view of the sample wafer 200 afterthe sample wafer 200 has been glued to the spacer wafer 810 andremounted on a copper support stub 800.

Transfer of the sample wafer 200 onto the spacer wafer 810 is done undera stereomicroscope using a vacuum wand with a fine-tipped needleattachment. The needle bevel is blunted for personal safety and tofacilitate handling the sample. A twenty millimeter (20 mm) long needle,gauge twenty three (23) to twenty six (26), is ideal for this and issmall enough that it does not swallow up the sample wafer 200. A specialfixture (not shown) may be used to hold the copper support stub 800, thevacuum wand, and the plan-view sample 200 during the remounting processin order to make the remounting process easier and faster.

FINAL SAWING PROCESS. The fourth stage in the method of the presentinvention comprises a final sawing process. The method of plan-viewsample preparation is completed by returning the remounted sample wafer200 to the TEMpro™ diamond saw. A software routine that is known as“Partial Process” is selected in order to avoid making a presaw cut. Sothe TEMpro™ diamond saw begins with a plan-view first saw cut. In thiscase the standard thirty micron (30 μm) cut is selected for theplan-view first saw width, as shown in FIG. 14.

The plan-view first saw cut is followed by a plan-view second saw cut toremove excess material from the sample wafer 200 and the spacer wafer810 and the copper support stub 800, as shown in FIG. 15. After theplan-view second saw cut has been completed the sample wafer 200 (andthe spacer wafer 810) and the stub holder fixture 310 are removed fromthe TEMpro™ diamond saw and an FIB clamp 1600 is attached to the samplewafer. The FIB clamp 1600 helps to hold the sample 200 in place during aplan-view third saw cut and also during subsequent FIB milling, as shownin FIG. 16.

Finally, the sample wafer 200, the stub holder fixture 310, and the FIBclamp 1600 are returned to the TEMpro™ diamond saw for a plan-view thirdsaw cut, as shown in FIG. 17. This is the last step in the final sawingprocess stage of the method and serves to completely sever the completedsample wafer 200 from the copper support stub 800. After the plan-viewthird saw cut the plan-view sample wafer 200 is ready for FIB millingand subsequent TEM imaging, as shown in FIG. 18.

The stages of the method of the present invention described above permitthe automated SELA process to be used for the automated preparation ofsite-specific plan-view TEM samples for semiconductor applications. ATEM sample that is output from the method of the present invention isready for plan-view FIB milling and is compatible with standard threemillimeter (3 mm) TEM sample holders. FIG. 19 shows an optical image ofa first side of a completed TEM sample with circuitry correctly orientedfor plan-view imaging. FIG. 20 shows an optical image of a second sideof the completed TEM sample shown in FIG. 19.

The processing time required for performing the method of the presentinvention is approximately forty (40) minutes. This amount of time isapproximately twice as long as the processing time required for thestandard SELA process for cross-sectional TEM samples. The processingtime required by the present invention represents a substantial timesaving when compared to the processing time required for the prior artmethods of preparing plan-view samples using tripod polishing. Theprocessing time required by the present invention also represents asubstantial time saving when compared to the processing time requiredfor the prior art method of polishing plan-view samples in preparationfor FIB milling.

The automated nature of the method of the present invention also allowslaboratory personnel to work on other tasks while the SELA tools areoperating. The possibility of the laboratory personnel being able to“multitask” in this manner does not exist in the case of the prior artprocesses (e.g., mechanical lapping-polishing).

FIG. 21 illustrates an exemplary TEM image of an FIB-milled plan-viewTEM sample manufactured in accordance with the method of the presentinvention. FIG. 21 shows a poly gate area and a source/drain area withsilicon dislocation loop defects.

FIG. 22 illustrates a flow chart 2200 showing the steps of anadvantageous embodiment of the method of the present invention. In thefirst step of the method a microcleaving process is performed toaccurately cleave an area of interest in a semiconductor wafer to createa sample wafer (step 2210). Then an initial sawing process is performedto prepare the sample wafer (step 2220). Then a remounting processremounts the sample wafer on a support stub with the sample waferoriented for plan-view imaging (step 2230). Then a final sawing processis applied to the remounted sample wafer to prepare the remounted samplewafer for FIB milling and subsequent plan-view TEM imaging (step 2240).

FIG. 23 illustrates a flow chart 2300 showing a more detailed version ofthe steps of a first portion of the method of the present inventionshown in FIG. 22. In the first step of the method an automatedmicrocleaver is used to accurately cleave an area of interest in asemiconductor wafer to create a sample wafer (step 2310). Then anautomated diamond saw (e.g., a SELA TEMpro™ automated diamond saw) tomake a pre-saw cut to remove excess material from the sample wafer (step2320). Then the sample wafer is automatically glued to a support stub(e.g., a copper support stub) (step 2330).

Then a first saw cut is applied to the sample wafer to make a shallowcut in the sample wafer (step 2340). Then a second saw cut is applied tothe sample wafer to cut through the sample wafer and the support stub(step 2350). Then the sample wafer is removed from the support stub(step 2360). Then a spacer wafer is glued to a new support stub (step2370). The sample wafer is then transferred to the spacer wafer (step2380). Control of the method then passes to step 2410 of FIG. 24.

FIG. 24 illustrates a flow chart 2400 showing a more detailed version ofthe steps of a second portion of the method of the present inventionshown in FIG. 22. Control of the method passes to the first step of themethod in FIG. 24 from step 2380 of FIG. 23. First the sample wafer isoriented for plan-view imaging (step 2410). As previously described, thesample wafer is rotated ninety degrees (90°) so that the circuitry onthe sample wafer is aligned properly for plan-view imaging. Then thesample wafer is glued to the top of the spacer wafer (step 2420).

Then the remounted sample wafer is returned to the automated diamondsawing tool (step 2430). The sawing tool is then used to apply aplan-view first saw cut to the remounted sample wafer to make a shallowcut in the remounted sample wafer (step 2440). Then the sawing tool isused to apply a plan-view second saw cut to cut through the remountedsample wafer and support stub (step 2450).

Then an FIB clamp is attached to the remounted sample wafer (step 2460).Then the sawing tool is used to apply a plan-view third saw cut to theremounted sample wafer to sever the remounted sample wafer from thesupport stub (step 2470). Then the remounted sample wafer is ready forFIB milling and subsequent plan-view TEM imaging (step 2480).

Although the present invention has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present invention encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. A method for preparing a sample wafer for plan view transmissionelectron microscopy, the method comprising: microcleaving a sample waferfrom a semiconductor wafer; cutting the sample wafer to expose a crosssectional view surface of a first remaining portion of the sample wafer;mounting a spacer to a support stub, and mounting the first remainingportion to the spacer in an orientation for plan view imaging; andcutting the first remaining portion to expose a plan view surface of asecond remaining portion of the sample wafer.
 2. The method of claim 1,wherein cutting the sample wafer comprises mounting the sample wafer ona first support stub.
 3. The method of claim 2, wherein mounting thefirst remaining portion comprises: removing the first remaining portionfrom the first support.
 4. The method of claim 3, further comprising:clamping a focused ion beam (FIB) clamp to a stub holder fixture thatsupports the second support stub; and cutting the second remainingportion of the sample wafer from the second support stub.
 5. The methodof claim 3, wherein mounting the first remaining portion on a secondsupport stub comprises rotating the first remaining portion by ninetydegrees.
 6. The method of claim 3, wherein the first remaining portionis mounted on the second support hub with a circuit of the firstremaining portion facing a wall of the second support stub.
 7. Thesemiconductor wafer test sample of claim 3, wherein mounting the firstremaining portion on a support stub comprises rotating the firstremaining portion by ninety degrees.
 8. A method for preparing a samplewafer for plan view transmission electron microscopy, the methodcomprising: microcleaving a sample wafer from a semiconductor wafer withan automated diamond sawing tool, the step of microcleaving furthercomprising, marking a selected location on the sample wafer with adiamond scribe, and cleaving the sample wafer at the marked locationwith the diamond sawing tool; cutting the sample wafer with theautomated diamond sawing tool to expose a cross sectional view surfaceof a first remaining portion of the sample wafer; mounting the firstremaining portion in an orientation for plan view imaging; and cuttingthe first remaining portion with the automated diamond sawing tool toexpose a plan view surface of a second remaining portion of the samplewafer.
 9. The method of claim 8, wherein cutting the sample wafercomprises: mounting the sample wafer on a first support stub; making afirst cut in the sample wafer using a first saw blade, wherein the firstcut does not cut through the sample wafer; and making a second cut inthe sample wafer using a second saw blade, wherein the second cut cutsthrough the sample wafer and the first support stub.
 10. The method ofclaim 9, wherein: mounting the first remaining portion comprises:removing the first remaining portion from the first support stub; andmounting the first remaining portion on a second support stub; andcutting the first remaining portion comprises: making a first cut in thefirst remaining portion using a first saw blade, wherein the first cutdoes not cut through the first remaining portion; and making a secondcut in the first remaining portion using a second saw blade, wherein thesecond cut cuts through the first remaining portion and the secondsupport stub.
 11. The method of claim 10, further comprising: clamping afocused ion beam (FIB) clamp to a stub holder fixture that supports thesecond support stub; and cutting the second remaining portion of thesample wafer from the second support stub with the automated diamondsawing tool.
 12. The method of claim 10, wherein mounting the firstremaining portion on a second support stub comprises: mounting a spacerto the second support stub; and mounting the first remaining portion tothe spacer.
 13. The method of claim 10, wherein mounting the firstremaining portion on a second support stub comprises rotating the firstremaining portion by ninety degrees.
 14. The method of claim 10, whereinthe first remaining portion is mounted on the second support hub with acircuit of the first remaining portion facing a wall of the secondsupport stub.
 15. A semiconductor wafer test sample prepared for planview transmission electron microscopy, the test sample manufactured by:microcleaving a sample wafer from a semiconductor wafer; cutting thesample wafer to expose a cross sectional view surface of a firstremaining portion of the sample wafer; mounting the first remainingportion in an orientation for plan view imaging on a support stub;cutting the first remaining portion and the support stub to expose aplan view surface of a second remaining portion of the sample wafer;clamping a focused ion beam (FIB) clamp to a stub holder fixture thatsupports the support stub; and cutting the test sample from the supportstub, wherein the test sample comprises a portion of the secondremaining portion of the sample wafer and a portion of the support stub.16. The semiconductor wafer test sample of claim 15, wherein mountingthe first remaining portion on a support stub comprises: mounting aspacer to the support stub; and mounting the first remaining portion tothe spacer, and wherein the test sample further comprises a portion ofthe spacer.
 17. The semiconductor wafer test sample of claim 15, whereinthe first remaining portion is mounted on the support hub with a circuitof the first remaining portion facing a wall of the second support stub.18. The semiconductor wafer test sample of claim 17, wherein the portionof the support stub comprises an imaging window.